Vapor discharge device



March 2l, 1933. Ml URlCH 1,902,110

VAPOR DISCHARGE DEVICE Original Filed July 3l 1929 3 Shets-Sheet l www@WMM@ MlCh 21, 1933. M. URlCH VAPOR DISCHARGEDEVICE Original Filed July5l, 1929 3 Sheets-Sheet 2 Original Filed July 31, 1929 3 Sheets-Sheet 3Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE MORITZ UBICH, 0FBADEN, SWITZERLAND, 'ASSIGNOR T0 'AKTIENGESELLSCHAFT BROWN BOVEBI CIE,OF BADEN, SWITZERLAND, A JOINT-STOCK COMPANY OF SWITZERLAND VAPORDISCHARGE DEVICE Application 111er! July 31, 1989, Serial No. 382,451. B.enewed January 24, 1933.

This invention relates to vapor discharge devices such as mercury vaporrectifiers and it has among its objects an improved construction ofmetal tank rectificrs permitting economies in manufacture and securingbetter operating performance. The objects and features of the inventionwill be best understood from the following description of anexemplification thereof, reference being had to the accompanying-drawings wherein, Y

Fig. 1 is a vertical sectional View along the line I-I of Fig. 2, of ametal tank rectifier embodying my invention;

Fig. 2 is a plan view of the rectifier shown in Fig. 1;

Fig. 3 is a detail vertical sectional view of the anode mounting alongline III-III of Fig. 2;`

Fig. 4 is a detail vertical sectional view of the tank structure of therectifier shown in Fig. 1;

Fig. -5 is a horizontal fragmentary sec- A tional view of the Weldedvertical joint of the tank along line V-V of Fig. 4; and,

Fig. 6 is a detail vertical sectional view of the 'oint between thecover and the side walls of t e tank.

The invention will be described as applied to a high power mercury arcrectifier of the metal tank type shown in the drawings, although in itsbroad aspects it is not limited thereto.

It comprises a hermeticallyy closed vessel including a main arc chamber1 and a condensing chamber 2 on the top thereof. The arc chamber 1 ismade of a steel cylinder 3 with a frustoconically shaped bottom plate 4anda substantially horizontal top plate 5. The bottom plate 4 has acentral opening 6 which leads to the mercury container 7 formed of ashort cylinder of insulating material such as porcelain that is closedat its bottom by a metallic cathode plate 8. A quantity of mercury 9within this container serves as the cathode of therectifier. The anodeplate 4 is likewise provided with a central opening over which ismounted the condensing chamber 2 referred to above. This condensingchamber is formed of a main cyla current interrupting arc at the surfaceof the cathode and thus start the operation of the rectifier.

Mounted circumferentially on the anode plate around the condensingchamber 2 are a plurality of anodes 15, usually six or a multiple of sixin number, depending on the capacity of the rectifier. Each anode 15 ismade in the form of a solid, heavy member of steel having rounded edgeswith a short reentrant portion at the lower end thereof. Each anode iscarried by a stem or lead 16 extending upwardly through the insulatingbushing 17 mounted within a suitable opening 18 in the anode plate. Theupper end of each anode stem is provided with a suitable lheat radiatingmember 19 for dissipating the heat generated at the anode during therectifying action, so as to maintain the anodes at the proper operatingtemperature. In addition to the main anodes there are also mounted onthe'anode plate 5 a pair of auxiliary anodes 21 by means of which arectifying arc may be maintained at the surface of the cathodeindependently of the operation of the main anodes 15.

The anode cylinder 3 and the bottom plate 4 thereof 'are surrounded by acooling jacket 25 through which water is circulated. The cylinder 11 ofthe condensing chamber 2 is likewise surrounded by a cooling jacket 26for circulating cooling water therethrough. The cathode bottom plate 8is made hollow and provided with a coolin space 27 through which waterlmay be circu ated. Similarly, the anode'plate 5 is made hollow' androvided with cooling spaces 28 through wiiich water may be circulated.The several cooling spaces are ordinarily connected in a coolingcircuit, the water being usually admitted to the hollow space 27 of thecathode through the inlet 29, and the water therefrom is' led throughthe connecting pipe 30 to the bottom of the cooling .jacket 25 to themain cylinder 3, wherefrom it passes through the connectother to providea hermetical enclosure and the interior of the vessel is highlyevacuated, as by means of a vacuum pump (not shown) connected to avalved exhaust opening 35 on the top of the condensing chamber. Forsatisfactory operation of the rectifier the cathode 9 must be heldinsulated from the remainder of the body of the rectifier vessel. It isalso important to protect the anodes of the rectifier against theinfluences tending to destroy the valve action of the anodes, and tothis end each of the anodes is enclosed in a relatively long, narrowshield 37 of metal, opening downwardly so as to prevent emanations fromthe cathode from reaching the space near the anodes.

There is also shown provided immediately underneath the opening into thecondensing chamber 2 a small collecting gutter 38 of metal forcollecting the condensed mercury trickling downwardly on the walls ofthe condensing chamber, the mercury being conveyed by a small pipe 39out of the path of the main arc to near the side wall of the main arcchamber from where it is permitted to trickle downwardly together withthe mercury condensing on the side walls of the chamber. The condensedmercury flows downwardly against the opening 6 and is returned to thepool 9 forming the cathode.

A strain ring 40 of metal with strain openings 41 is mounted on thebottom plate 4 in front of the cathode opening 6 and serves to collectimpurities and solid particles gathered up by the mercury trickling downtowards the cathode, the impurities being retained and the mercury beingpermitted to pass through the openings 4l towards the cathode 9.

`The problem of constructing an operative and satisfactory high powermetal tank rectifier baflied the electrical art for many years and evenup to the present, the construction of satisfactory 'high power metaltank rectifiers is extremely difficult.4 The matter of greatestimportance for satisfactory rectitiers is the provision of hermeticallyclosed large metal vessels capable of maintaining the high degree ofvacuum which is absolutely essential for the maintenance of therectifier action, and avoidance of destructive back-firing. In addition,it has been found that the entire interior of the vessel and allthe-parts whichv come in contact with the mercury vapor, must bemaintained free from impurities or what may be described as in aperfectly sterile condition. These requirements, coupled with theobscure phenomena he rectifier shown in the drawings embodies a numberof features which greatly simplify the diliiculties in constructing suchapparatus and eliminate to a large extent the underlying causesresponsible for much of the troub e encountered with the prior artconstruct-ions.

One of the features of my invention resides 1n the novel construction-ofthe rectifier vessel itself. The only practical way found heretofore formaking the large hermetically tight steel vessels required for a mercuryarc rectifier is to form the several parts of sheet steel and weldtogether the sheet parts into a closed vessel. For the operativeness ofthe device it is of course essential that the welded joints be perfectlytight and capable of preventing leakage into the vessel against thenormal vacuum within the interior of about 1/800,000 of an atmosphere.In making such vacuum tight welded joints one has to depend entirely onthe skill of the operator and as the welding itself is an extremelyerratic process and difficult to control, one can never be sure whetherthe welded joints are good or not until they have been against vacuumtightness.

Prior to my invention, in order to make sure of the vacuum tightness ofthe vessel it has been the practice to assemble the entire vesselstructure and examine minutely the entire vessel with regard to thetightness of the welded joints. The usual procedure was to place theentire vessel into a container with water and pump into the interior ofthe vessel compressed tight, no bubbles would be formed under the water.The formation of bubbles indicated that the vessel was leaking at somepoint and the entire vessel had to be scrutinized to determine the pointof leakage. rlhis was often done by the soap water test, ing appliedover the individual portions ol" the vessel and compressed air pumpedinto the interior of the vessel. On the tight portions of the vessel nosoap bubbles would form, and the formation of soap bubbles indicatedthepoints where the vessel was not tight. As a rule, these points ofleakageoccurred at the welded joints of the vessel parts, the main bodyof the sheet metal being almost always air-tight. v

This system of testing the vessel joints for air tightness was not onlycumbersome, ex-

pensive and slow, but proved also to be danpractically tested air. Ifthe vessel was soap water bev explosion, the parts thrown apart by thecom- 153 pressed air would hit persons near the vessel causing seriousinjury t0 them.

The vessel construction of my invention permits the construction ofwelded large metal tank rectifier vessels and the examination of theindividual parts and the individual vjoints for vacuum tightness withoutnecessitating the assembly of the entire vessel structure for thepurpose of examination.

According to my invention, the entirev vessel is made of a suiiicientnumber of detachable parts so as to permit each part to be readilycleaned and examined for cleanlinessbefore assembling it into the closedvessol structure. Because of the requirement for vacuum tightness, theindividual parts arewinade of rolled iron or some similar material thathas passed through the rolling operation, the rolling action closing upany pores that the material might have had originally and therebysubstantially assuring that there Will be no leakage throughthe body ofthe material used for the parts. As a rule, such rolled sheet materialcannot be directly formed into the shape and size required for thevessel. I accordingly weld the sheet metal parts into the required shapeand size and make the individual joints with what I term hollow welds.This hollow weld is made essentially by Welding the sections to bejoined on opposite sidesand leaving a hollow space or groove between thetwo welds.

I then test each individual part so made for the vacuum tightness of itswelded joints without going to the trouble of assembling the entirevessel as was done heretofore. The procedure followed by me consistsessentially in pumping compressed air or similar substance into thehollow spaces of the welds of the individual parts and applying soapWater over the welded joints. If the weld is satisfactory and vacuumtight, no soap bubbles will form on either side of the weld and the ointis then assuredly vacuum tight. If soap bubbles are formed in any of theparts of the Weld, the weld can be readily repaired as the part isdisassembled and readily accessible, until a ycompletely vacuum tightWeld has been obtained. In this manner defects at a welded joint arereadily detected and the individual parts of the rectifier vessel madein themselves perfectly airtight.

In the prior art constructions it was often necessary to repeat theperformance of assembling the vessel and testing it for vacuum tightnessa number of times, once a joint of one part of the vessel showing afault, and then a different point of the vessel showin a fault, and thenagain imperfections deve oping in the repair of the faults previouslydetected, and so on. Such procedure would. often require daysindetecting one fault after another, it being necessary to assemble .takeit apart and reassemble it until all the the entireveel each time for atest and then faults, sometimes large in number, have been found andcorrected. By my invention all these di'iculties are removed andfurthermore, the danger to the persons working on the manufacture of thedevice and in the sursides of the hollow weld groove.

It is of course understood that the-method of testing the individualparts and the individual joints of auch parts for vacuum tightness, asdescribed above, is not the only one suitable for carrying out myinvention. In

its broad aspects this feature of my invention contemplates the testingof the vacuum tightness of the individual welded joints of the vessel bymaking such welded joints in the forni of hollow spaces or channels anddetermining the air-tightness of such hollow channels in any approvedand satisfactory way in which the air-tightness of a hollow vessel canbe determined. g

I shall now describe the construction and procedure of m invention inconnection with the exempl' cation shown in the drawing. The main andmost` diicult part of the vessel is the enclosure forming the mainrectifier chamber 1. The cylindrical part 3 of this enclosure is formedof a substantially rectangular sheet of iron suitably bent intocylindrical shape and joined lengthwise where the longitudinal edges 45meet by a hollow weld referred to before and shown in detail in Figs. 4and 5. To this end, the edges themselves are directly welded to eachother by a layer of filler material 46 such as iron, the material beingdeposited along the edges in any of the forms usually "approved forweldinv operations.

As siown in the drawings, the abutting ed of the sheet metalcylinder 3are prefera ly slightly tapered on both sides so as to facilitate thedeposit of the filler material, and a layer of the iller'material isapplied on both sides of the vtapered edges. When this operation iscompleted, there is welded over the outside o f the longitudinal weld 46a channel shaped strip of iron 47 forming a longitudinal hollow channel48 over the outside of the weld 46, the channel shaped member beingwelded at 4 9 and 50 to each of the joints 46 form the hol owlongitudinal welded joint of the tlinder 3. To the top of the icylinder3 so ormed there is welded the top aie 51. This to cylinder flange ismade Y in eV form of a eavy steel r' adapted to lit directly above theopening o the sheet cylinder 3 and to be joined thereto, the flangehaving for this purpose a downward extenvsion 52 as shown in Figs. 4 and6.

The upper edge of the sheet metal cylin- 5 der 3 fits into a. somewhatenlarged opening 53 at the lower side of the flange 51, the side wallsof said opening constituting shoulders against which the cooperatingportions at the upper end of the cylinder 3 abut. At the l0 corner wherethe aforementioned side walls of the flange opening 52 meet, there isprovided in the flange a hollow circular groove 54l which surrounds theupper end of the cylinder 3 and constitutes the weld channel by means ofwhich the vacuum tightness of the joint between the flange and thecylinder 3 is determined.

The flange 51 and the cylinder 3 are joined to each other by circularwelds at the place 55 where the inner side of the cylinder 3 meets theabutting flange wall and at the place 56 where the outer wall of thecylinder 3 meets the lower extension 52 of the flange 51. There is thusformed a hollow welded joint between the upper end of the cylinder andthe upper cylinder flange 51, with a hol. low circular channel 54extending through the entire length of the welded joint and with twowelded junctions 55, 56 on both sides of the hollow weld channel 54.

The abutting wall 54 of the cylinder 3 is slightly dished orfustoconically shaped and may be made either by directly pressing a flatsheet metal plate into the desired shape as shown in the drawing, or bysuitably cutting an annular plate section and welding it together alongtwo radially abutting edges..

In the exemplification shown in the drawings the bottom plate 4 is madeof a single plate pressed int-o the form shown in the drawings, thecentral portion of the plate being provided with an opening and havinthe central portion forged to form a flange 5 for securing the cathodecylinder thereto. The outer periphery of the bottom wall 4 is providedwith a circular hollow weld groove 58 and the wall portions of bothsides of the cathode are welded at 59 and 60 to the lower outer andlower inner edges of the cylinder 3 of the vessel.

There are further provided communicating connections between thelongitudinal hollow channel 48 of the longitudinal welded joint of thecylinder 3 and the two circular weld grooves 54 and 58 through theperforations 62 and 63, respectively, in the flange'extension 52 and theedge of the cylindrical wall 3. at the points above and below thelongitudinal weld channel 48.

00 In the practical manufacture, the flange 51 and the bottom wall 4 arewelded tothe cylindrical wall 3 as explained above, and the hollow weldchannel piece 47 is then welded in place so as to provide a hermeti- 66cally closed communicating connection be-I tween the upper weld channel54'and the lower weld channel 58. An external commanicating connection'with the hollow spaces formed by the Weld channels is provided through abore 64 drilled into the flange 51 over the outside rim thereof, and aconnecting bore 65 between the channel 54 and the bore 64. Theperforation 64 is threaded at its outer end and is adapted to receivethe threaded bolt 66 by means of which the hollow spaces of the weldsmay be closed up or to receive a pipe connection through which asuitable pressure fluid may be pumped or applied to the channels fordetermining the vacuum tightness of the joints.

The cylindrical vessel Apart so made may be readily tested for thevacuum tightness of the joints by connecting to the threaded end of theperforation 64 a compressed air supply admitting air of a given pressureinto the hollow spaces formed between the circumferential andlongitudinal welds of the vessel. Compressed air will then fill thecircular channel 54, the longitudinal channel 48 and the circularchannel 58 of the welds. Soap water applied over these welds willreadily indicate whether there is any fault at any particular point ofthe welds, soap bubbles forming at the points where the welds are nottight. If a fault is found, the fault may be readily'corrected and thetest repeated right in place until the welded joints are all perfect andall leaks are eliminated. This work can be done on the cylindrical partof the vessel alone without assembling it with the other parts, therebygreatly simplifying the manufacture of the rectifying vessel. After theWelded joints khave thus been found to be satisfactory, the

air is released from the hollow weld channels and the channel space ispermanently closed up by means of the bolt 66 threaded over the openinginto the channel space.

Combined with this main rectifying cylinder'is the hollow cover 5 on thetop thereof. For the satisfactory operation of the rectifier it isimportant to keep the cover at a relatively low temperature so as tosecure effective condensation of the vapor within the rectifier chamberand maintain the seals around the anode lead-ins in operative condition.In the construction shown in the drawings, the hollow anode plate 5 isformed by welding an upper sheet metal plate 71 and a lower sheet metalplate. 72 to the mem# bers forming the outer flange ring 73, the

inner flange ring 74, and the anode lead-in outer flange ring 73 and the,inner flange ring 74- have approximately the shape shown lin thedrawings except that the sealing grooves onthe lower side of the flangering 73 are turned in place after the plate has been completely welded.

The members forming the anode bushing rings 75 have the outer contour asshown in the drawing in Fig. 4, the inside of these members being solidand the anode o enings 18 being made after the plate has een completelywelded.

T e upper and lower plates 71 are prepared with openings and cut so asto fit between the rings 73 and 74 and over the anode bushing memtbers75, and the several parts are then welded to one another alon the joints76, 77, 78, suitable filler material geing deposited in the groovesprovided at the points of junction so as to secure a good fusion of theparts and a hermetically tight weld. In this way there is formed ananode plate with a hollow space between the upper and lower sheets 71and 72, the hollow space enclosing the anode bushing member 75 andpermitting the circulation of water therethrough for cooling the anodeplate and the parts going therethrough as explained before.

The central ring 74 of the anode plate has a central opening 81 to whichis welded at 82, 83, the lower end of the cylinder 11 constituting thecondensing chamber. The upper end of the cylinder A11 is similarlyjoined to the condensing chamber cover plate 12 by a weld at 84 andeventually also at 85, although on account of the small size of thisjoint the inner weld 85 may as a rule be dispensed with, a singleoutside weld 84 being usually sufficient. The upper side of the centralring 74 is provided with an enlarged opening 84a which constitutes acommunicating channel through which water from the anode plate passesinto the condensing chamber jacket 26. This condensing chamber jackethas at its lower end a flange ring 86 fitting over the opening 84 of thecentral anode plate ring 74, and the upper end of the condensing chamberjacket 26 is provided with a flange ring 87 fitting over thecircumference of the condensing chamber cover 12 adapted to be clampedto it by means of bolts 88. The flange ring 86 is preferably welded tothe condensing chamber jacket 26 at 89 and the upper flange ring -87 maybe similarly welded to the jacket 26 The openings 32 through which theanode plate communicates with the condensing chamber jacket 26 are madeby drilling a number of holes in the central anode plate ring '74. Thecondensing jacket 26 is arranged so as to be detachably removable fromthe condensing chamber walls 11 after unscrewing the bolts 88, whichhold it in place. A good, tight connection is provided between thecondensing jacket and theadjacent portions of the anode top plate andthe condensing chamber by means of packing rings 91 and 92 wed d betweenthe engagin surfaces of the con ensing jacket parts an the condensingchamber top and anode plate ring 74. By screwing down the bolts 88 theengaging surfaces are tightened against the rubber packing rings 91 soas to provide a tight jolnt at these places.

The anode platc may be readily tested for the vacuum tightness of thejoints by simpl plugging up the holes 32 at the center and a mitting airunder pressure into the hollow space while at the same time applyingsoap water over the various welded joints, thereby detecting any faultywelds. In a similar way, the weld between the condensing chamber clinder 1l and the central anode plate ring 4 may be tested by means ofthe hollow weld groove 93 provided between the welded joints 82 and 83.

Where trouble is experienced in making a tight welded joint between therelatively small condensing chamber cover 12 and the upper end-of thecondensing chamber cylind er 11, the tightness of this welded joint maylikewise be tested and secured by providing a hollow weld groove 94between the welded joints 84 and 85 of the condensing chamber and coverplate. Usually I find it unnecessary to check up separately thetightness of the welded joints of the anode plate 5 and of thecondensing chamber cylinder 11. Instead I proceed as follows: I completethe anode plate and weld in place the condensing chamber cylinder 11 andcomplete the jacket for the condensing chamber and screw it in place. Ithen admit compressed air into the hollow spaces within the anode plateand the condensmg chamber jacket through one of the water inlet openingsafter having plugged up the other openings and apply the soap water testto the welds. This enables quick detect1on of any faults in the weldsbetween the condensing chamber and the anode plate and of the anodeplate itself, without necessltatlng separate testing of the welds of theanode plate per se and of the welds of the condensing chamber to theanode plate and to the condensing chamber cover.

The cathode plate 8 is likewise made by welding several parts togetherto forni a hollow body, the plate consisting of an upper member 95forming a shortI cylinder, tothe lowerbpen end of which has been weldedthe bottom wall 96 along the annular joint 97. The hollow cooling spacefor the cathode plate is thus provided in an economical way whilesecuring a'rigid and substantial construction.

A distinct feature of the construction shown in the drawings is the newform of joint between the anode plate flange 73 and the flange 51 of thecylindrical vessel 3. The essential requirement is of course that thejoint shall be vacuum tight just as the other Y rectifiers which are nowjoints of the vessel. The provision of a vacuum tight joint of suchenormous length yas that between the circumference of the anode plateand the abutting portion of the cylinder flange 51, suitable for mercurarc rectliers, is however an extremely comp icated and difficult matter.The ordinary acking materials generally used for securmg detachablevacuum tight joints between metal parts cannot indiscriminately be usedon mercury arc rectiiers because materials that tend to vaporize underthe high temperature at which these vessel portions operate, wouldquickly destroy the vacuum within the interior of the vessel and producebackfire or in general render the apparatus inoperative. Many of theworkers engaged in the construction of mercury arc rectiiers attemptedto reduce this difficulty of large detachable vacuum tight joints byeliminating the detachable joint between the anode plate cover and thetop end of the vessel, making the top of the vessel with the side wallsthereof as a single solid unit. Such construction of course reduces thedifficulty of providing the large detachable vacuum tight joints butrenders it more ditlicult to clean the individual parts of the rectilierbefore assembling, and to maintain them in the required highly sterilecondition referred to before, and necessary for avoiding backfiretroubles or other disturbances in the operation of the rectifier.

In the rectifiers of the type shown in the drawings it has been thepractice to use a mercury seal at the joint between the anode plate andthe top of the cylindrical rectifying chamber. This mercury seal isobtained by providing a hollow channel along the joint with tightlypressed sealed surfaces on both sides of the hollow channel, the hollowchannel being filled with mercury so as to provide a liquid vacuum tightseal over the solid sealing surfaces. In order to make such sealspossible there must of course be provided a solid sealing joint betweenthe abutting surfaces on the side of the sealing channel leading to therectifier chamber, of such nature as to prevent the mercury from beingdrawn into the rectifying chamber under the action of the vacuumtherein.

Various materials had been tried in the past to provide such a solidsealing joint between the abutting surface portions but heretofore theonly satisfactory type of joint consisted of an asbestos packing clampedbetween the adjacent steel surfaces of the cover and the cylinderflange. As long as the opening that -is to be sealed is relatively smallthe provision of such asbestos packing rings does not meet any seriousdiiliculties. However, with the large dimensions of high capacity beingchiefly constructed, it was almost impossible to provide an asbestospacking ring of the enormous diameter required to seal up the jointsbetween the anode -plate' and the cylinder Y flange 51. Asbestos packinof the t pe suitable for mercury arc recti ers have ittle coherence andbecome readil disjointed, introducing small leakage c annels throughwhich the mercury filling the (space gradually leaks estroying theoperativeness of the rectifier and causing endless trouble in itsoperation.

There are on the market a number of organic packing materials that donot have the aforementioned disadvantages of asbestos packings. Chiefamong these materials is rubber, which by itself constitutes anexcellent packing substance for sealing up the inside joints of mercuryseals. However, rubberand similar organic packing materials proved to bevery unsatisfactory 1n mercurly arc rectiiers when used at the jointswhic open directly into the interior of the vessel because suchmaterials develop-large quantities of vapors when operated at the temeratures at which the associated parts o the vessel are practicallymaintained, the developed vapors destroying the vacuum within thevesselland producing backfire.

In the construction shown in the drawings there is emplo ed a novel typeof sealing joint between the anode plate and the vessel which makes itpossible to use rubber packing while preventing direct exposure of therubber packing to the interior of the evacuated space and therebylargely eliminating the undesirable effects resulting from directexposure of rubber packing to the vacuum space .0f the vessel. This ismade possible by so constructing the joints that i-n the course of theoperation of the vessel a seal of mercury forms itself over the edge ofthe rubber packing which would ordinarily be exposed to the mterior ofthe vessel so that in fact, not the rubber packing but a mercury sealforms the enclosure of the evacuated space at the sealing joints. y

As seen in Figs. 4 and 6, the inner edge of the cylinder flange 51 isprovided at its upper horizontal face with two annular upwardlyextending sealing rings 101 and 102. The adjacent horizontal surface ofthe anode flange 73 is provided with correspondingly shaped grooves 103,104, the sealing rings extending into the grooves. Between the outerlower surfaces of the sealing rings 101, 102, and the adjacent lowerring portions of the anode top flange 7 3 there are placed two rubberrings 105. 106, so that on clamping the top' plate against the flange 51a tight joint will be produced between the rubber rings 105, 106 and theportions on the top flange 103 and cylinder flange 51 in engagementtherewith. An annular hollow sealing channel 107 is thereby formedbetween the two rubber rings 105, 106, which hollow sealing channel isfilled with mercury that constitutes hollow sealing into-the vessel,often Vthe vacuum seal between the interior of the vessel and theoutside thereof. v

The inner sealing ring 101 of the seal so obtained extends for a certainheight above the upper edge of the innerrubber ring 105 and forms ahollow annular trap 109. iVhen the top is tirst assembled in place onthe cylinder this hollow trap 109 is empty and the upper edge of therubber ring 105 is directly exposed to the interior of the vessel.

As is well known, metal tank mercury arc rectifiers require a certainforming period during which the entire vessel is heated while at thesame time a strong evacuation is carried on so as to drive oif all thegases from the parts of the vessel opening into the interior of thechamber. uring this formative period the rubber ring 105 will give .off

a good many excess gases and vapors which will be evacuated, but inthe-.course of the formation there will slowly be formed condensedmercury in the hollow trap 109 above the rubber ring until the entireannular groove of the trap 109 is filled with a layer of mercury whichthus acts as a self-forming, self-maintaining protective layer betweenthe rubber ring 105 and the interior of the vessel. As the adjacentparts of the vessel portions are strongly cooled, there will always becondensed mercury at these portions of t e vessel and there will usuallybe sufficient mercury in the trap 109 to eliminate the possibility ofany serious damage to the' vacuum condition of the vessel by reason ofthe use of rubber as the internal packing ring for the mercury seal ofthe anode plate.

The above described anode plate seal construction is very simple tomanufacture and gi ves highly satisfactory results and has been found tohe much more economical than the constructions used prior thereto.`

The construction shown is also of advantage when using an asbestospacking ring as the internal packing ring 105 as with this circularscaling ring construction it is much casier to .secure a good packingbetween the sealing edges of the anode plate and the cylinder fiange 51than with the constructions of the prior art.

'hile l have described the use of the novel sealing arrangement inconnection with rubber packing rings it is of course understood that myinvention is not restricted to the use of this material and that othermaterials 55v of similar characteristics may be used instead.

In Fig. 6 there is also shown communicating channels 111 drilled intothe fiange 51 of the anode plate by means of which the effectiveness ofthe mercury seal 107 is checked up,`a small gauge such as shown at 112being connected to said opening. The level of the mercury in the gaugeindicates whether there is enough mercury in the hol- 65 low space 103to secure suilicient sealing acleak through into arrangement could ofcourse be used for this y purpose.

The construction of the anode seals of the rectifier shown in thedrawing likewise embodies improvements which are of great advantage overthe prior art.

As shown in Fig. 3, the anode bushing 17 is held in place within itsassociated opening 18 in the anode plate by means of a suitablysectionalized retaining ring 120 secured to the under side of the anodeplate around the plate openin 18. The anode bushing 17 has its upper ensomewhat enlarged to provide a shoulder 121 which rests on this anoderetaining ring, a washer 122 of packing materfal such as asbestos beinginterposed between the bushing shoulder and the rin The opening 18 ofthe anode plate throug which the bushing 17 extends is made somewhatwider than the part of the bushing passing therethrough to provide asealing space 125 which tapers down at the bottom to substantially thewidth of the bushing 17 itself. The bottomof this sealing spaceA 125 isfilled with a suitable packin 126 such as asbestos down, with a 4layer osomewhat more solid packing material such as an asbestos cord 126constituting the lower foundaton for the packing. This circular packing126 is compressed and held in the compressed state by means of astuffing bushing 127, the upper end of which extends above the upperlevel of the anode plate 5. A loose flange ring 129 is mounted overthetop of thel stuing bushing 127 and is arranged to be .drawn downagainst the anode plate 5 by means of bolts 130 disposedcircumferentally along the fiange.

Packing rings 131 and 132 are clamped by the flange 1.29 against thestuiing bushing 127 on one side and against the anode bushing and anodeplate on the other side, respectively, so as to provide a tightenclosure at the upper side of the sealing space 125 around the anodeinsulator bushing 17.

The stuliing bushing'fiange 129 is provided with a groove or channel 134along the upper outer edge of the stufiing bushing 127 and the bushingitself has a bore 135 through which communication is provided betweenthe groove 134 and the sealing space 125. This groove 134 in turn isconnected through a bore 137 in the bushing flange 129, with a mercurygauge 138 in the form of alittle mercury-filled tube threaded into anopening 139 on the top of the ange and communicating witlithe bore 137.The sealingspace 125 is filled with mercury by pouring it into the bore137 by way of the opening 139 and a continuous check-up of the presenceof the mercury possible a very substantial simplification of themanufacture of this very sensitive seal and effects a reduction in thetime and cost of the manufacture of these parts. In addition,

. it reduces the space required for mounting the individual anodes ofthe anode plate, thereby enabling closer mounting of the an-` odes thanwith the prior art construct1ons.

The anode stem 16 extends over the interior of the anode bushing 17 andis threaded at its upper end projecting above the bushing, the threadedportion being secured within the radiator core 141 that 1s provided witha downward cylindrical extension 142 surrounding the anode stem 16. Theupper end of the anode bushing 17 has an enlarged opening providing asealing space 143 for the inner anode seal. The lower end of thissealing space 143 is closed up by a packing 144 similar to the packing126, a stuffing bushing 145 with a flange 146 and rubber packing rings147, 148 completing the enclosure of the in- `ner anode sealing space143. This sealing space is filled with mercury and the mercurycontinuously maintained therein by means of a mercury gauge 149 in theway described in connection with gauge 138.

The anode 15 itself is held clamped against the lower end of the bushing16 by the action of the nut 151 threaded around the upper end of thecore extension 142, a spring 152 being interposed between the nut andthe flange 146 to prevent cracking of the bushing and to take upexpansion of the parts under variations of temperature.

As seen in Figs. 1 and 4, the cathode insulator 7 has fiat upper andlower sealing surfaces pressed against fiat sealing surfaces at thelower end of the flan e 57 of the bottom plate of the rectifying c amberand on the cathode plate 8. Circular sealing grooves 155, 156 areprovided along the upper and lower sealing surfaces of the cathodeinsulator 7, these grooves being provided in the insulator itself or onthe sealing surfaces of the m'etal parts that are in engagementtherewith. These sealing grooves 155, 156 are held tight and enclosed bymeans of packing rings 157 and the spaces within the grooves are filledwith mercury, the mercury being Imaintained within the grooves andchecked up by means of gauges 157 connected through tubings 158, 159with the sealing grooves 155, 156, respectively.

l As the cathode sealing surfaces are rather extensive and the energylosses at the cathode are relatively large, the portions of the vesseladjacent to the cathode sealing grooves 155, 156, andthe associatedsealing surfaces are so arranged 'as to be `eXposed to efficient coolingaction. As seen 1n the drawings, the A cathode plate 8 is made so thatthe entire part of the plate 8 underlying the seal with the lower end ofthe cathode insulator 7 is cooled by water circulated through the hollowcathode plate. In the preferred arrangement, I usually lead the coolingwater first into the hollow cathode plate space 27 so as to obtain thegreatest cooling action at this part of the vessel. In like manner, theflange 57 at the center of the bottom wall 4 of the rectifying chamberis so shaped as to cause'the cooling water to circulate directly overthe upper -side 161 of the flange portion that is in engagement with theupper sealing surface of the insulating ring 7.

There is further provided a circular defiector sheet 162 within thecentral portion of the water jacket 25 on the under side of the bottomplate 4, the deflector being so arranged that the relatively cool waterentering the lower end of the jacket first passes over the coolingsurface 161 of the upper mercury seal 155 of the cathode ring beforecontacting with the walls of the chamber bottom 4. A very effectivecooling action at the sensitive cathode seal is thus maintained withoutcomplications inthe construction or in the layout of the cooling systemfor the rectifier.

The construction of the rectifier described above and the variousfeatures thereof were reached only as the result of years of developmentwork in the face of countless difficulties which very often jeopardizedthe entire development of this important power apparatus. As explainedbefore, the entire rectifier vessel of the present invention may bebuilt of separate parts made up with welded joints, the individual partsbeing arranged for testing of the vacuum tightness of their jointswithout necessitating the assembly of the parts into a complete,enclosed vessel. The individual parts so made are assembled into aunitary, hermetically closed structure readily maintained in vacuumtightcondition by the liquid seals at the detachable joining surfaces.The entire vessel may thus be made of parts which are readily inspectedand permit very close cleaning and sterilizing of the interior portionsof the vessel. All the joints are extremely simple and readilymanufactured and readily maintained in operative condition.

` The various features of the invention described and claimed herein arenot limited to theparticular constructional details referred to in thespecification for the purpose of exemplification as many othermodifications thereof will suggest themselves to those skilled in theart. It is accordingly desired that the appended claims be given a broadconstruction commensurate with the scope of the invention within theart.

I claim:

1. An evacuated space-discharge device comprising a metallic rectifyingvessel haviner a plurality of detachable sections hermeticdlly joinedone to the other, seals of liquids at the junctions of said sections, atleast one of said sections having a hollow welded joint on its interiorWall.

2. An evacuated space-discharge device comprising an evacuated metallicrectifying vessel having a plurality of sections detachably joined oneto the other, seals of liquid at the junction surfaces of said sections,the individual metal portions constituting the walls of said vesselbeing double-walled to provide .hollow spaces aroundthe surfaces exposedto the interior of the chamber, and means whereby the individualsections may be examined for vacuum tightness by determining the vacuumtightness of the hollow space surrounding the inner wall of therespective section.

3. An evacuated space-discharge device comprising a hermetically closedevacuated metalic rectifier vessel comprising a plurality of adjoiningmetallic sections, seals of liquid vat the junctions of said sections,at least one of said sections having on its interior wall a weldedjoint, said welded joint forming a hollow channel having we`.dedjunctions on the sides of said channel, and means for testing the vacuumtightness of the hollow channel formed between the welded junctions.

4. An evacuated space-discharge device comprising a hermetically closedmetallic rectilier vessel having a sheet metal cylinder, and a bottomplate united to said. cylinder by a welded joint exposed to the interiorspace of said vessel, said welded joint comprising a hollow channel atthe junction points of said sections with welded junctions on both sidesof said channel, and means for determining the vacuum tightness of thehollow space of said channel.

5. An evacuated discharge device comprising, a hermetically closedmetallic vacuum vessel comprising a wall section formed of a sheet metalcylinder having a longitudinal joint on its interior side, a weldedjunction on one side of said joint, a welded junction on the other sideof said joint, said welded junctions being spaced from each other topro- A vide a hollow groove therebetween, and a connection fordetermining the vacuum tightness of said hollow groove.

6. An evacuated space-discharge device comprising an evacuated metallicvessel having a cylindrical wall section, longitudinal w-elds on saidcylindrical 4section exposed to the space in the interior of saidvessel, said longitudinal welds comprising a welded junction, on the.inner side of saidI cylinder and a welded junction on the outer side ofsaid cylinder opposite said first welded junction, said welded junctionsbeing relatively spaced from each other to provide a hollow ooveextending throughout the length o said junctions, and a connection tosaid hollow space for determining the vacuum ti htness thereof.

An evacuated space-discharge device comprising a rectigying vesselhaving sheet metal sections j oine one to the other to form a-vacuumtight enclosure, welded junctions between some of the adjacent sheetmetal sections exposed to the interior .of said enclosure, andlongitudinally extending hermetically closed grooves along said weldedjunctions. f v

8. An `evacuated space-discharge device comprising aV rectif ing vesselhaving sheet metal sectlons j oine one to the other to form a vacuumtight enclosure, welded junctions between s ome of the adjacent sheetmetal sections on the interior sides thereof, longitudinally extendinghermetically closed grooves along said welded junctions, and aconnection to said grooves for determining the vacuum tightness of thehollow spaces therein.

9. A mercury arc rectifier, comprising a rectifying vessel having sheetmetal sections joined one to the other to form a vacuum tightenclosure,joints between some of the' adjacent sheet `metal sectionshaving longitudinal welded junctions on the inner side of the metallicsheet body exposed to the interior of the enclosure, and similarjunctions on the other side of said metallic sheet body, said weldedjunctions on both sides of the sheet body being spaced from each otherand .arranged to form a hollow longitudinal groove extending along thejunction, and a connection for determining the vacuum tightness Iof thehollow channel formed between said welded junctions.

10. The method of constructing a hermetically closed evacuatedrectifying vessel which comprises constructing a plurality of vesselsections adapted to be detachably joined one to the other to form aclosed vessel, making at least some of said sections of welded sheetmetal bodies, with a hermetically closed hollow space around the weldedjoints, and determining the vacuum tightness of the hollow space soprovided prior to the assembling of the individual parts into thecomplete vessel.

11.6The method of constructing a metallic hermetically closed evacuatedvessel of the vacuum type for electrical space discharge devices whichcomprises the construction of a plurality ofvessel sections of sheetmetal, making at least some of said section by welding sheet metalbodies to each other, with longitudinal hollow grooves extending alongthe welded joints of said sections, and determining the vacuum tightnessof the welded joints so made by determining the vacuum tightness of thehollow grooves along. said welded joints independently ofthedetermination of the hermetical tightness of the assembled vessel as awhole. l

12. An evacuated vdischarge device comprising an evacuated vessel havinga pair of vessel sections adapted to be detach'ably joined to each otheralong cooperating junction surfaces, said junction surfaces beingsubstantially flat and parallel to each other,I

one of said junction surfaces having a pair of upstanding projections,the other of said junction surfaces having a pair of grooves adapted toreceive said upstanding projections, a strip of packing materialdisposed `near the bottom of the groove formed by said having a tubularvessel section, saidI tubular' vessel section having on its inner wallswelded joints running in circumferential and longitudinal directions,said welded joints forming hollow channels having welded junctions onboth sides of the channels, the channels of said circumferential andlongitudinal joints being inter-connected to constitute anintercommunicating hollow space, and a connection `for determining thevacuum-tightness of said intercommunicating hollow space.

14. n evacuated discharge device comprising a hermetically closedvessel, an electrode seal therefor comprising a metallic vessel sectionhaving a tubular opening, a hollow insulating bushing extending throughsaid opening, an electrode lead sealed through the interior of saidbushing, a packing strip on the interior side of said tubular opening, astuiling bushing surrounding said insulator bushing for compressing saidpacking strip and holding it in engagement with the surfaces of saidinsulating bushing and the adjacent wall section of said tubularopening, a flange surrounding the upper end of said stuffing bushing,means for clamping said flange over said stuiing bushing, packing ringson the inner and outer sides of the upper end of said stuiiing bushingto provide an enclosed annular channel around said insulating bushingwithin said tubular opening, a sealing liquid container disposed on saidflange having a duct connection extending through said flange betweenthe inner and outer packing ring into said annular channel formaintaining therein a liquid seal.

.MORITZ URICIL

